Early optical fiber communication systems typically used opto-electronic pulse regenerators, referred to as "repeaters". Regeneration involved detection of an incoming optical pulse, amplification, re-shaping and re-timing of the resulting detector output, and generation of the outgoing optical pulse. This approach was relatively expensive but otherwise satisfactory as long as the communication systems had relatively low bit rates. However, the above-referred to optoelectronic re-generation provides a bottleneck that has to be overcome before very high speed (e.g., data rates above about 40 Gb/s per channel) systems could be installed.
The development of optical fiber amplifiers was an important step towards elimination of the opto-electronic bottleneck. However, such amplifiers do not provide pulse shaping and re-timing.
All-optical processing is the key to overcoming the opto-electronic bottlenecks in high-speed communications networks. In particular, as the technology heads towards bit rates of 100 Gbits/s per channel in transparent communication systems, all-optical pulse regeneration is widely recognized as an important replacement for conventional electronic repeater technology.
Beside optical limiting and clock recovery, pulse re-shaping is one of the main concerns of optical pulse regeneration.
During propagation of an optical pulse from transmitter to receiver of an optical fiber communication systems, fiber-intrinsic properties such as dispersion and non-linearities are responsible for pulse distortion both in the temporal and the spectral domain. As a consequence, the bit error rate of the system is significantly increased in both time division multiplexed (TDM) and wavelength division multiplexed (WDM) systems. Thus, it would be desirable to have available all-optical means for pulse reshaping. Desirably, such means would be compact, adjustable, wavelength selective and cost effective, and would be applicable to any dispersive, nonlinear optical fiber communication system. This application discloses such means, and communication systems that comprise such means. M. Nakazawa et al., Electronics Letters, Vol. 29 (9), p.729, April 1993, disclose a soliton transmission system wherein the transmission fiber is soliton transmission fiber with average negative group velocity dispersion of -0.4 ps/km/nm. The system is selected to maintain the pulses as soliton pulses throughout, with the soliton peak power of a fundamental (N=1) soliton being as low as 0.65 mW, and the average soliton period being as long as 935 km. J. K. Lucek et al., Optical Letters, Vol. 18 (15), p. 1226, August 1993, disclose an all-optical signal regenerator comprising a nonlinear fiber loop mirror. S. Bigo et al., IEEE J. of Selected Topics in Quantum Electronics, Vol. 3 (5), p. 1208, October 1997 disclose soliton regeneration by means that comprise a nonlinear optical loop mirror. B. J. Eggleton et al., Optics Letters, Vol. 22(12), p. 883, June 1997, disclose all-optical switching and pulse reshaping in long-period fiber gratings that couple light between co-propagating core and cladding modes. B. J. Eggleton et al., Physical Review Letters Vol. 76 (10), p. 1627, March 1996, disclose the observation of nonlinear propagation effects in fiber Bragg gratings, resulting in nonlinear optical pulse compression and soliton propagation. They also disclose soliton formation in periodic structures.
For background on optical solitons see, for instance, "Optical Fiber Telecommunications", Vol. III A, Chapter 12, pp. 373-460, L. F. Mollenauer et al.; "Optical Solitons-Theory and Experiment", R. Taylor, editor, Cambridge University Press, 1992, especially pp. 30-37 and 80-81; and "Nonlinear Fiber Optics," 2.sup.nd edition, G. P. Agrawal, Academic Press, (1995), especially pp. 42-43 and 144-147.
All references cited herein are incorporated herein by reference.